This invention relates to a fiber optics duplex module for bidirectional simultaneous transmission and receipt of light signals to and from a common optical fiber channel or link, and more particularly to such a module in which crosstalk between the transmitter and receiver is minimized.
Communication via optical fibers is a rapidly developing technology, as exemplified in U.S. Pat. No. 3,953,727. Advantages of using optical fibers versus conventional microwave cables are many, but most significant are the weight and volume reductions which can be realized. In spite of the greater capabilities of an optical fiber communication system, present schemes do not utilize the full system capacities due to the inherent problem of crosstalk between transmit and receive signals when using a common optical channel.
In order to obtain satisfactory levels of isolation between the transmitter and the receiver at the end of an optical fiber link, techniques are employed which effectively reduce the efficiency of the system to fifty percent or less of its full potential. One of these techniques is the use of separate fiber links for the transmit and receive channels. Another method employed is time multiplexing wherein the receiver is turned off while the transmitter is broadcasting and vice-versa.
If a common fiber or fiber bundle can be used to simultaneously transmit and receive signals, the efficiency of operation of the system can be significantly improved. The problem has been, however, the high degree of isolation between the transmit and receive signals that is required in order to enable use of such a duplex system in a long-range application where any spillover or crosstalk from the transmit signal would tend to swamp out the relatively weak receive signal characteristic of such long-range use. The duplex module of the present invention is aimed at greatly reducing, if not eliminating, the primary source of crosstalk between the transmitter and the receiver in behalf of affording such bidirectional simultaneous communication by way of an optical fiber link of lengths heretofore considered to be impractical.